Major property improvements are obtained in injection molded articles prepared using molds wherein one of the mold elements is rotated during and after the injection of the plastic into the mold cavity by the process described in U.S. Pat. No. 3,907,952. A difficult problem in constructing injection molds suitable for this process is in the forming of a good seal along the parting line of the mold to prevent flashing. For example, conventional seals formed between highly machined surfaces under clamping pressure are generally poorly adapted to this type of mold since the seal interface is not static.
U.S. Pat. No. 3,500,503 discloses that a gap seal, i.e., a seal formed by non-touching contact between closely adjacent surfaces, can be used effectively to seal an injection mold cavity. A technical drawback of a gap seal, however, is that exceedingly exact and reliable preciseness of the gap dimension is essential for commercial utility since a malfunction of the seal generally disables the mold.
Accordingly, it is an objective of the present invention to provide an improved seal of the type characterized by maintaining a gap of exceedingly fine tolerance and which effectively seals an injection mold cavity along the mold parting line in apparatus wherein one element of the mold is rotatable.
It is a further objective of this invention to provide such a seal assembly which is unitized and relatively easily installed and replaced to minimize maintenance problems related to seal malfunctions.
It is still a further objective of the invention to provide a seal structure of the described type which is preloaded under compression, and which may accept further loading and variances in the loading thereof in an injection mold caused by cyclic or other factors, with minimal tendency to disturb the critical dimension tolerance of the gap seal.
These and other objectives of the invention are obtained in a rotary seal and bearing assembly suited for use in an injection mold wherein one of the mold elements is rotatably driven, the rotary seal and bearing assembly comprising a seating ring, the seating ring being adapted to seat about the mold cavity at the mold part line, a seal ring having an annular sealing face within the seating face of the seating ring and being recessed therefrom to define a narrow annular gap with the peripheral edge of the mold cavity with the assistance of said seating ring, one of said rings being journable with respect to the other of said rings, said rings being floatable in the axial direction as a unit against a resilient member, and means for preloading the seating ring, seal ring and resilient member under a preload compressive force.